Patch "usb: misc: legousbtower: Fix NULL pointer deference" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

usb: misc: legousbtower: Fix NULL pointer deference

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
usb-misc-legousbtower-fix-null-pointer-deference.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Greg Kroah-Hartman <[email protected]>
Date: Mon, 19 Sep 2016 19:09:51 +0100
Subject: usb: misc: legousbtower: Fix NULL pointer deference

From: Greg Kroah-Hartman <[email protected]>

commit 2fae9e5a7babada041e2e161699ade2447a01989 upstream.

This patch fixes a NULL pointer dereference caused by a race codition in the probe function of the legousbtower driver. It re-structures the probe function to only register the interface after successfully reading the board's firmware ID.

The probe function does not deregister the usb interface after an error receiving the devices firmware ID. The device file registered (/dev/usb/legousbtower%d) may be read/written globally before the probe function returns. When tower_delete is called in the probe function (after an r/w has been initiated), core dev structures are deleted while the file operation functions are still running. If the 0 address is mappable on the machine, this vulnerability can be used to create a Local Priviege Escalation exploit via a write-what-where condition by remapping dev->interrupt_out_buffer in tower_write. A forged USB device and local program execution would be required for LPE. The USB device would have to delay the control message in tower_probe and accept the control urb in tower_open whilst guest code initiated a write to the device file as tower_delete is called from the error in tower_probe.

This bug has existed since 2003. Patch tested by emulated device.

---
 drivers/usb/misc/legousbtower.c |   35 +++++++++++++++++------------------
 1 file changed, 17 insertions(+), 18 deletions(-)

@@ -898,24 +898,6 @@ static int tower_probe (struct usb_inter
 	dev->interrupt_in_interval = interrupt_in_interval ? interrupt_in_interval : dev->interrupt_in_endpoint->bInterval;
 	dev->interrupt_out_interval = interrupt_out_interval ? interrupt_out_interval : dev->interrupt_out_endpoint->bInterval;
 
-	/* we can register the device now, as it is ready */
-	usb_set_intfdata (interface, dev);
-
-	retval = usb_register_dev (interface, &tower_class);
-
-	if (retval) {
-		/* something prevented us from registering this driver */
-		dev_err(idev, "Not able to get a minor for this device.\n");
-		usb_set_intfdata (interface, NULL);
-		goto error;
-	}
-	dev->minor = interface->minor;
-
-	/* let the user know what node this device is now attached to */
-	dev_info(&interface->dev, "LEGO USB Tower #%d now attached to major "
-		 "%d minor %d\n", (dev->minor - LEGO_USB_TOWER_MINOR_BASE),
-		 USB_MAJOR, dev->minor);
-
 	/* get the firmware version and log it */
 	result = usb_control_msg (udev,
 				  usb_rcvctrlpipe(udev, 0),

@@ -936,6 +918,23 @@ static int tower_probe (struct usb_inter
 		 get_version_reply.minor,
 		 le16_to_cpu(get_version_reply.build_no));
 
+	/* we can register the device now, as it is ready */
+	usb_set_intfdata (interface, dev);
+
+	retval = usb_register_dev (interface, &tower_class);
+
+	if (retval) {
+		/* something prevented us from registering this driver */
+		dev_err(idev, "Not able to get a minor for this device.\n");
+		usb_set_intfdata (interface, NULL);
+		goto error;
+	}
+	dev->minor = interface->minor;
+
+	/* let the user know what node this device is now attached to */
+	dev_info(&interface->dev, "LEGO USB Tower #%d now attached to major "
+		 "%d minor %d\n", (dev->minor - LEGO_USB_TOWER_MINOR_BASE),
+		 USB_MAJOR, dev->minor);
 
 exit:
 	return retval;

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/usb-misc-legousbtower-fix-null-pointer-deference.patch queue-4.8/arm64-debug-avoid-resetting-stepping-state-machine-when-tif_singlestep.patch queue-4.8/using-bug_on-as-an-assert-is-_never_-acceptable.patch